Optical disc and apparatus for scanning the optical disc

ABSTRACT

An optical disc is described for recording data, which disc has a recording area subdivided in coaxial annular zones comprising circular or spiral tracks. Each track within one of the zones is arranged for storing a same predetermined amount of data, and the first track of each zone stores an amount of data proportional to the radial position, resulting on average in a substantially constant density, the so called CLV (Constant Linear Velocity) density. The tracks comprise periodic characteristics, e.g. a wobble, which are radially aligned within each one of the zones, the periodicity being indicative of the track recording density for the track concerned. Hence the data recording and reading speed can be synchronised to the periodic characteristics, whereas any cross-talk of the periodic characteristics of neighbouring tracks is avoided.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 09/366,693 filed Aug. 4,1999 now U.S. Pat. No. 6,603,729; which is hereby incorporated herein inwhole by reference.

FIELD OF THE INVENTION

The invention relates to the field of optical disk data storage andretrieval.

BACKGROUND OF THE INVENTION

The invention relates to an optical disc including a recording area forrecording data at a substantially constant density, the recording areabeing subdivided in a plurality of coaxial annular zones includingcircular or spiral tracks, each track within one of the zones forstoring a same predetermined amount of data at a track density, theaverage of the track densities within one zone being substantially equalto the constant density.

The invention further relates to a recording device for recording dataat a substantially constant density on an optical disc including arecording area having circular or spiral tracks, which recording area issubdivided in a plurality of coaxial annular zones, which deviceincludes a recording head and recording control apparatus.

The invention further relates to a read device for reading data from anoptical disc recorded at a substantially constant density, the opticaldisc including a recording area having circular or spiral tracks, whichrecording area is subdivided in a plurality of coaxial annular zones,which device includes a reading head and read control means.

Such a record carrier and apparatus are known from European PatentApplication EP 0 587 019, herein document D1. The document discloses arecord carrier in the form of an optical disc having a recording areaincluding a pattern of grooves on a substrate, constituting aservopattern of circular or spiral tracks. The recording area issubdivided in coaxial annular zones, and within a zone each trackincludes the same amount of data. Hence the density of data storagedecreases when going radially outward, whereas at the start of the nextzone the density is restored. The average density over the entiresurface is substantially equal, usually called a CLV (Constant LinearVelocity) density, e.g. as used in the audio CD. However within a zonethe amount of data in each turn of the track is constant, usually calleda CAV density (Constant Angular Velocity). The disc comprises a numberof radially aligned servo pits in each turn, constituting a so-calledsampled servo pattern. The servo pattern including radially alignedelements is called Constant Angular Velocity (CAV) servo pattern, and isto be scanned by a servo system having a phase locked loop (PLL) togenerate a servo frequency locked to the rotation frequency of the disc.The servo pits are dimensioned to be read clocked by said servofrequency. Further a data phase locked loop is provided for generating adata clock locked to a speed of data read/write operations, which areperformed at the substantially constant linear density. When jumping toa new radial position, the rotation frequency setting point or the dataclock setting point are adjusted to the new position, but the servophase locked loop remains locked to the CAV servo pattern. Hence theservo pits are always read at the servo frequency. The recordingapparatus including an optical system for recording or readinginformation by generating a spot via a radiation beam on a track of therecord carrier. The optical disc is rotated and the spot is positionedin radial direction on the centre of the track by servo means forscanning the track. During scanning the servo phase locked loop islocked to the rotation frequency of the disc for reading the CAV servopattern. The data phase locked loop is locked to the CLV data speed. Theknown record carrier and apparatus have the problem, that for reliableoperation a first phase locked loop must be locked to the CAV servopattern, and a second phase locked loop must be locked to the CLV datadensity. Those skilled in the art are also directed to U.S. Pat.4,901,300, herein document D2.

The above references are hereby incorporated herein in whole byreference.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an optical disc, a recordingand a reading device arranged for a more reliable data recording and/orretrieval operation while data is recorded at a substantially constantdensity.

An optical disc has tracks that include periodic characteristics whichare radially aligned within each one of the zones, the periodicity beingindicative of the track recording density for the track concerned. Thishas the effect, that the speed of data recording and reading can bedirectly locked to a signal generated by detecting the periodiccharacteristics. When jumping within a zone the speed is not changed,whereas when jumping to a different zone the speed changes by a knownamount. There is no need for a second phase locked loop, only one phaselocked loop locked to the data frequency is required. Hence, therecording is less complex and more reliable.

A recording device has recording control apparatus arranged fordetecting the periodic characteristics and for recording dependingthereon a same predetermined amount data in each track within one of thezones at said track density. A reading device has read control apparatusarranged for detecting the periodic characteristics and for readingdepending thereon a same predetermined amount data from each trackwithin one of the zones at the track density. This has the effect, thatdata, although positioned corresponding to a CAV pattern within a zone,has on average substantially the CLV density, and can be recorded andread by apparatus directly synchronized to a signal generated bydetecting the periodic characteristics.

The invention is also based on the following recognition relating to thereliability of the detection of servo signals in high density opticalrecording. For achieving the high density the distance between tracks,the track pitch, is designed as small as possible for the availablescanning system and scanning spot size. When servo elements, e.g. pitsor other periodic track characteristics, are then scanned and a servosignal is generated, the servo elements of neighbouring tracks alsoinfluence the servo signal, which is called cross-talk. However for aCLV density the amount of data stored in a track must be increasedradially. The inventors have seen that by aligning the periodiccharacteristics within a zone the cross-talk within the zone can beeliminated. At the start of the next zone the density is increasedstepwise, so that on average the density is substantially equal to theCLV density. The cross-talk problem is now only present at the boundarytrack between two zones. The boundary track can be skipped, or specialcountermeasures can be taken to control the interference problems at thezone boundary.

In an embodiment of the optical disc, is the size of zones is such thatthe difference in the number of periodic characteristics in a turn ofthe track at the boundaries of adjoining zones is relatively low inrelation to the number of periodic characteristics in a turn of thetrack. A difference in periodicity causes an interference patternincluding (partial) extinctions in a boundary signal generated from theperiodic characteristics when scanning a track at the boundary of twozones. A low difference in relation to the periodicity results in theboundary signal having only a few extinctions, which can be positionedby selecting the phase difference of the periodic characteristics.

BRIEF DESCRIPTION OF THE DRAWING

These and other aspects of the invention will be apparent from andelucidated further with reference to the embodiments described by way ofexample in the following description and with reference to theaccompanying drawings, in which

FIG. 1 shows a record carrier,

FIG. 2 shows a prior art optical disc with a CLV header pattern,

FIG. 3 shows a zoned optical disc,

FIG. 4 shows a header and sector layout,

FIG. 5 shows an apparatus for reading a record carrier,

FIG. 6 shows an apparatus for writing and reading a record carrier,

FIG. 7 shows a land/groove servo pattern at a zone boundary,

FIG. 8 shows an optical disc having a wobbled track, and

FIG. 9 shows servo signals generated at a zone boundary. Correspondingelements in different Figures have identical reference numerals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1a shows a disc-shaped record carrier 1 having a track 9 intendedfor recording and a central hole 10. The track 9 is arranged inaccordance with a pattern of turns constituting substantially parallelspiral tracks. The track 9 on the record carrier is indicated by apre-embossed track structure provided during manufacture of the blankrecord carrier. The track structure includes, for example, by apregroove 4 which enables a read/write head to follow the track 9 duringscanning. The invention is applicable in a corresponding manner to othertrack patterns having substantially parallel tracks, in which the turnsare concentric instead of spiral forming circular tracks.

FIG. 1b is a cross-section taken along the line b—b of the recordcarrier 1, in which a transparent substrate 5 is provided with arecording layer 6 and a protective layer 7. The pregroove 4 may beimplemented as an indentation or an elevation, or as a material propertydeviating from its surroundings. The recording layer 6 may be opticallyor magneto-optically (MO) writable by a device for writing information,for example, as in the known CD-Recordable system. During writing, therecording layer is locally heated by a beam of electromagneticradiation, such as laser light. The recording layer in a re-writablerecord carrier contains, for example, a phase-change material whichacquires an amorphous or crystallized state when it is heated to thecorrect extent.

FIG. 1c shows an alternative track structure consisting of alternatingelevated and deepened tracks, called lands 11 and grooves 12. It is tobe noted, that both lands 11 and grooves 12 serve as recording tracks.Each turn has at least one area interrupting the lands and groovesconstituting a header area. For a spiral pattern, the grooves may becontinued as grooves once in each turn after the header areaconstituting a double spiral by the concatenated lands and theconcatenated grooves. Alternatively, at least once per turn, atransition from land to groove or vice versa is established by switchingto the other type after the header area.

According to the invention, the tracks are subdivided in recordabletrack portions 3 by radially aligned headers 2. The track portions 3 arefor reading or recording optical marks representing user information,and are preceded by the headers for individually accessing each trackportion. The headers include position information indicating theposition of the header and the adjoining track portion relative to thebeginning of the track or radial and angular parameters, e.g. addressmarks representing address information. Address marks on a recordabletype of record carrier are usually embossed during manufacture to enablepositioning of a read/write head anywhere on the still unrecorded recordcarrier. The headers are located at a few, e.g. four, angular positionsin each turn of the track, which corresponds to the header locationsused in the Constant Angular Velocity (CAV) system. However the positioninformation in the headers at the CAV locations is written at CLVdensity, i.e. the marks are encoding the position information at aconstant density. This is schematically indicated by the rectangularheader areas 2 in FIG. 1a. Due to the CAV location of the headers, thetrack portions have a length proportional to the radial position, i.e.the distance to the middle of the central hole 10. The track portionsare recorded at a constant density, and therefore the amount of data ina track portion is proportional to the radial position, called the CLVformat. The data within the track portions and the position informationin the adjoining header are recorded at the same density and can be readwith the same reading apparatus. Data to be recorded is subdivided insectors of a fixed length, which are recorded from a first arbitraryangular and radial position to a second arbitrary position, thepositions being in between headers. In the disc format, according to theinvention, there is no requirement to have a number of sectors fittingexactly in a turn, which gives additional advantages in average datadensity, because no zoning or small zones can be used. The arbitrarypositions can be calculated according to a few formula's knowing theamounts of data recordable in each track portion. Hence, a reducedheader overhead is achieved using a few CAV aligned headers per turn andwriting sectors at CLV data density, which sectors are not aligned tothe headers.

FIG. 2 shows a prior art optical disc 21, such as DVD-RAM, using a zonedCLV format (CLV=Constant Linear Velocity, i.e. constant recordingdensity independent of the radial position). Headers 22,23,24 areprovided for each sector, and the recording area of the disc issubdivided in coaxial annular zones. Each track portion within one ofthe zones, accommodates one sector, and the associated header includes aphysical address for that sector. Each zone has a fixed number ofsectors in a turn, and the number of zones increases by one for eachradially outward next zone. The headers 24 of the first sector in eachturn are aligned radially. The further headers 22,23 are aligned withinthe zone, and within the zone the amount of data recorded in a turnremains constant according to the CAV system (Constant AngularVelocity). The format of this disc is called ZCLV (Zoned CLV). Howeverthe prior art ZCLV disc has a significant loss of data storage capacitydue to the large amount of headers. This loss is referred to asoverhead, which overhead is reduced by the invention.

FIG. 3 shows a zoned optical disc according to the invention. The dischas a recording area 31 from an inner diameter 32 to an outer diameter33. The recording include circular or spiral tracks (as shown in FIG. 1)and the tracks are interrupted by headers 34 forming track portions. Theheaders are radially aligned, in particular the beginning of the headersis aligned along straight radial lines 36. The recording area 31 of thedisc is subdivided in coaxial annular zones, and within each zone thetrack portions are arranged for recording a same amount of data. Withina zone, the density starts at a nominal level, say the CLV density, anddecreases proportional to the radial position of the track portionconcerned, and at the beginning of a next zone the density is set to thenominal level. Hence the density within each zone is according to theCAV system. The average density of the total recording area is a littlebelow the nominal CLV level, such a zoning loss being dependent on thenumber of zones, e.g. larger with only a few large zones. Hence, eachtrack portion within one of the zones is arranged for recording a samepredetermined amount of data at a track portion density, and the averageof track portion densities within one zone is substantially equal to theCLV density. The headers are written at the data density, whichdecreases outwardly within a zone according to the CAV system, theending portions 35 of the headers are aligned at radial line-pieces 35at a different angle constituting a sawtooth like structure on eachspoke. In an embodiment of the disc, the track portions are providedwith periodic characteristics indicative of the density for therespective track portion. During scanning in a reading device, theperiodic characteristics generate a periodic signal in a scanning unit,e.g. in the servo signals or the data reading signal. The periodicsignals can be used to synchronize the data recording or reading, e.g.by a phase locked loop circuit locked to the periodic signal. Theperiodic characteristics may be a variation of the track position in adirection transverse to the track called a wobble, or other variationsof width or depth of the track. A track wobble for a CLV disc withoutheaders, e.g. a CD-R, is described in U.S. 4,901,300 document (D2). Inan embodiment of the zoned disc, according to the invention, the trackwobbles within a zone are radially aligned. The number of wobbles withina track portion is constant, and a fixed amount of data corresponds toone wobble, e.g. one wobble is 324 channel bits, and a frame is 6wobbles or 1944 channel bits or 155 data bytes for a given channel code.

FIG. 4 shows a header and sector layout. FIG. 4a shows a land/groovepattern interrupted by headers in an enlarged and schematic way. A firstgroove 41 is interrupted by a header area 40. A first land 42 radiallyadjoins the first groove 41, and further grooves and lands follow. Thegrooves are provided with a transversal variation of the location, theso-called wobble, which is aligned between grooves. The header area issubdivided in a first portion 43 used for groove headers and a secondportion 44 for land headers. Hence the reading of address marks 45representing the position information is not disturbed by interferencefrom address marks in a radially neighbouring area.

FIG. 4b shows a header and track portion layout indicating the logicalassignment of information stored. The unit of length is the wobbleperiod, which corresponds to a fixed amount of channel bits as explainedabove. First a header are 40 is given, subdivided in a groove headerportion 43 and a land header portion 44. Thereafter a 5 wobble controlportion 46 follows for controlling the reading of stored data. Thecontrol portion 46 is subdivided in a Gap (non written area directlyadjoining the header area), a Guard area for starting the writingoperation (some variation in the starting point allowed to preventwear), a VFO area for locking a Variable Frequency Oscillator, and aSYNC pattern for logically synchronising the channel code. After thecontrol portion 46, a DATA area 47 follows for storing the user data,which DATA area has a length depending on the radial position of thetrack portion. The last part 48 of the track portion, before the nextheader area, is subdivided in a PA, a Post Amble for closing the channelcode encoding, a second Guard and Gap with similar function as Gap andGuard in the control portion 46.

FIG. 4c shows the logical data format. User data is subdivided insectors 142 of a fixed length of 2 kByte, which each, for example,require 98 wobbles when recorded. A number of sectors, e.g. 32, arejoined together forming an ECC block, in which Error Correcting Codesare included for correcting errors anywhere in the ECC block. Such along ECC block provides better protection against burst errors, andconstitutes the minimum amount of data to be written. Also, if only onesector must be changed, the full ECC block is to be rewritten includingnewly calculated error codes. A linking sector 141, which is only a fewwobbles, is reserve as buffer in between ECC blocks to allow independentwriting of such blocks. Usually, the linking sector is written withdummy data to make sure that no intermediate blank areas remain.Obviously, the ECC block does not fit in a track portion, the block maybe larger or smaller then the DATA area 47 within a track portion. Theactual start of an ECC block can be easily calculated from the length ofthe block, the block address and the size of the track portions, whichvaries in a predetermined way depending on the radial position. Thecalculation gives a track number, a header number within the track and adistance from that header, e.g. expressed as a number of wobbles. In anembodiment of the optical disc, the position information in the headerincludes a track number indicating the radial position of the track andheader number indicating the angular position of the header. It is to benoted, that a specific header will always be within a block with aspecific address and there will always be located a next block at aknown distance from that header. In an embodiment of the optical disc,the position information in a header includes a block address indicatingthe block locatable at the header and a next block indicator indicativeof the distance from the header to the start of the next block. Theblock address may be the block starting before and including the header,or it may be the address of the next starting block.

FIGS. 5 and 6 show reading apparatus according to the invention forscanning a record carrier 1. The scanning apparatus of FIG. 5 arearranged for reading the record carrier 1, which record carrier isidentical to the record carriers shown in FIG. 1 or FIG. 3. The deviceis provided with a read head 52 for scanning the track on the recordcarrier and read control apparatus including drive apparatus 55 forrotating the record carrier 1, a reading unit 53, for example, includinga channel decoder and an error corrector, tracking apparatus 51 and asystem control unit 56. The read head includes an optical system of aknown type for generating a radiation spot 66 focused on a track of therecording layer of the record carrier via a radiation beam 65 guidedthrough optical elements. The radiation beam 65 is generated by aradiation source, e.g. a laser diode. The read head further includes afocusing actuator for focusing the radiation beam 65 on the recordinglayer and a tracking actuator 59 for fine positioning of the spot 66 inradial direction on the centre of the track. The tracking actuator 59may includes coils for radially moving an optical element or may bearranged for changing the angle of a reflecting element on a movablepart of the read head or on a part on a fixed position in the case partof the optical system is mounted on a fixed position. The radiation:reflected by the recording layer is detected by a detector of a usualtype, e.g. a four-quadrant diode, for generating a detector signals 57including a read signal, a tracking error and a focusing error signal.The read apparatus is provided with tracking apparatus 51 coupled to theread head for receiving the tracking error signal from the read head andcontrolling the tracking actuator 59. During reading, the read signal isconverted into output information, indicated by arrow 64, in the readingunit 53. The read. apparatus is provided with an header detector 50 fordetecting the header areas and retrieving address information from thedetector signals 57 when scanning the header areas of the tracks of therecord carrier. The header detecting apparatus 50 are arranged forreading the position information from the headers substantially at thedata density, which substantially corresponds to the constant densityused in CLV. The apparatus has positioning apparatus 54 for coarselypositioning the read head 52 in the radial direction on the track, thefine positioning being performed by the tracking apparatus 59. Thedevice is further provided with a system control unit 56 for receivingcommands from a controlling computer system or from a user and forcontrolling the apparatus via control lines 58, e.g. a system busconnected to the drive apparatus 55, the positioning apparatus 54, theheader detector 50, the tracking apparatus 51 and the reading unit 53.To this end, the system control unit includes control circuitry, forexample, a microprocessor, a program memory and control gates, forperforming the procedures described below. The system control unit 56may also be implemented as a state machine in logic circuits. It is tobe noted, that the headers are located at CAV positions, and thereforethe amount of data in the track portions is dependent on the radialposition. The reading unit 53 is arranged for eliminating the headersfrom the data read, which eliminating may be controlled via the controllines 58 by the header detector 50. Alternatively, the reading apparatusare provided with deformatting apparatus, which recognize and remove theheaders and further control information from the data stream.

In an embodiment, the read device is arranged for reading a disc havingcontinuous wobbled tracks, as described below with reference to FIG. 8.The read control apparatus are arranged for detecting the periodiccharacteristics and for reading depending thereon, a same predeterminedamount of data from each track within one of the zones. A read clock issynchronized to the periodic characteristics and the reading unit 53reads a fixed number of channel bits for each instance of the periodiccharacteristics. In an embodiment, the read control apparatus arearranged for retrieving the data from an area of the track following anunrecorded area. The read clock is synchronised to the periodiccharacteristics in the unrecorded area, and hence, the reading speed isadjusted during scanning the unrecorded area.

The system control unit 56 is arranged to perform the positioninformation recovery and positioning procedure as follows. A desiredblock address is derived from a command received from the user or from acontrolling computer. The position of the block expressed in a tracknumber and header number and distance from the header is calculatedbased on the known amounts of data stored in each track portion. A tablemay be used for a zoned format, giving for each zone the first blockaddress and the length of the track portions, which is fixed during azone. The radial distance from the current position to the desired tracknumber is determined and a control signal is generated for positioningapparatus 54 to radially move the read head 52 to the desired track.When the radial movement is completed, a header is read by the headerdetector 50. The read signal of the header is processed to detect, ifthe desired track is being read. If so, the system control unit waitsuntil the arrival of the desired header. After this header any databefore the calculated distance from the header is discarded, and datafrom the desired block is read from a linking position within thelinking sector described with reference to FIG. 4c. In practice all datastarting at the header will be read, and any data before the start ofthe requested block will be discarded, and for reading the linkingposition is effectively equal to the start of the block.

Preferably, the system control unit 56 is arranged for combining thefirst amount of data from a first track portion with at least onefurther amount of data read from a consecutive track portion, the atleast one further amount of data including a final amount of dataretrieved from a track portion up to a next linking position. Hence, thetotal ECC block includes a first amount from part of the first trackportion-read, a final amount from part of the last track portion read,and as much intermediate amounts from track portions between the firstand last track portion.

FIG. 6 shows a device for writing information on a record carrier,according to the invention, of a type which is (re)writable in, forexample, a magneto-optical or optical manner (via phase change or dye)by using a beam 65 of electromagnetic radiation. The device is alsoequipped for reading and including the same elements as the apparatusfor reading described, above with FIG. 5, except that it has awrite/read head 62 and recording control apparatus which include driveapparatus 55 for rotating the record carrier 1, a write unit 60, whichinlcudes, for example, a formatter, an error coder and a channel coder,tracking apparatus 51 and a system control unit 56. The write/read head62 has the same function as the read head 52 together with a writefunction and is coupled to the write unit 60. The information presentedto the input of the writing apparatus 60 (indicated by the arrow 63) isdistributed over logical and physical sectors according to formattingand encoding rules and converted into a write signal 61 for thewrite/read head 62. The system control unit 56 is arranged forcontrolling the writing apparatus 60 and for performing the positioninformation recovery and positioning procedure as described above forthe reading apparatus. During the writing operation, marks representingthe information are formed on the record carrier. Writing and reading ofinformation for recording on optical discs and usable formatting, errorcorrecting and channel coding rules, are well-known in the art, e.g.from the CD system. In particular, the header detecting apparatus 50 arearranged for reading the position information from the headers,substantially at the data density, which substantially corresponds tothe constant density used in CLV. In the recording device or the readingdevice, the header detecting apparatus are synchronized to a data clock,which clock is generated by clock generation apparatus. The data clockis also used to control the writing apparatus 60 and/or the reading unit53. The clock generation apparatus can be controlled by the systemcontrol unit 56 based on the radial position, the zone and the rotationrate of the disc. In an embodiment of the device the clock generationapparatus includes a phase locked loop, for example, accommodated in theheader detection apparatus, which phase locked loop is locked to theperiodic characteristics of the track, such as the wobble, duringscanning. After a jump of the head 52,62 to a new scanning location theclock generation apparatus may be preset to the data clock value at thenew location, or the bandwidth of the phase locked loop may be increasedto lock quickly to the new wobble frequency. Hence the recording controlapparatus are arranged for detecting the periodic characteristics andfor locking the phase locked loop to the periodicity thereof. Apredetermined, fixed number of channel bits is recorded corresponding toeach instance of the periodic characteristics, and as within a zone thenumber of periodic characteristics in a turn of the track is constant, asame predetermined amount data in each track within one of the zones.

FIG. 7 shows a land/groove servo pattern at a zone boundary. The tracksmarked L (land) and G (groove) are to be scanned from left to right andare connected via a spiral (not shown) to the left side of the Figure.The tracks are provided with wobbles or other preformed variationsindicate the track portion data storage density. A first groove track 71is the last track of a first zone and has a wobble corresponding to thedata density in that zone, the last part of the first groove track beingshown on the left side of the Figure. After the interruption by headerarea 70, the first groove track 71 continues as second groove track 73belonging to the next zone, which is provided with the wobble accordingto that next zone, and hence the intermediate land track 72 forms thezone boundary 74. From zone to zone the number of wobbles in a trackportion may be increased, e.g. by 1 wobble or by a frame of 6 wobbles.In the land/groove format, the wobble is implemented in the groove, andon the land the wobbles of both neighbouring grooves are added in theservo signal. On the land 72 between two zones, there is in interferencebetween the two wobbles of slightly different period, e.g. when thenumber of wobbles in a track portion is increased by one frame (6wobbles) at a zone boundary, the servo signal will be extinct to zerosix times. The advantage of having only one wobble increase per trackportion at a zone boundary is, that only one extinction of the servosignal occurs. Having one or only a few extinctions in a boundary trackportion gives a sufficiently long area before a header where the servosignal is present at a sufficient amplitude to keep the phase lockedloop in lock. Hence, reading of the header is possible also at theboundary track portions and even recording data in such track portionsis possible. Alternatively, the boundary track portions may be skipped,and even at least one header directly following a boundary turn. Theservo signal of land track 72 has an interference of the two differentwobbles and is not easily usable for data storage. Additional measuresmay be taken in the recording and reading device to counter the effectsof the interference, but in a practical embodiment the land track 72 isnot used for data storage for a full turn, the unused turn forming thezone boundary 74. It is to be noted, that on the boundary 74 the firstland header 76, the second land header 77, etc. up to the last landheader 78 cannot be reliably read because of the interference. In anembodiment of the disc (for reliable operation) two additional headersare not used, resulting in an unused track at eight headers in a turn.In an embodiment of the disc (for symmetry reasons, i.e. the same totalstorage capacity for land and groove) the capacity of the groove tracksis limited also by skipping the same amount of groove tracks at eachzone boundary, shown in FIG. 7 as the groove track 73.

FIG. 8 shows an optical disc 1 having a wobbled track. The recordingarea 81 is subdivided in three coaxial, annular zones 82, 83 and 84.Each zone is provided with wobbled, circular or spiral tracks 85. Theinner zone 84 has, for example, n wobble periods, the middle zone 83 hasn+8 periods, and the outer zone n+16 periods. The numbers of wobbles andthe increase are selected for drawing purposes only. The number ofperiodic characteristics at the start of a zone has to be proportionalto the radial distance to the centre of the disc. By selecting theappropriate size of the zones, the difference in the number of periodiccharacteristics from zone to zone may be selected to be low relative tototal number of periodic characteristics in a turn. For example, for alarge number of zones (100), a difference of only a few wobble periods(1% for a radial range of diameter n to 2n) from zone to zone can beachieved. The resulting signal has the a strong component related to theperiodicity (e.g. the wobble frequency), and is amplitude modulated witha relatively low frequency due to the cross-talk or summation of signalsfrom neighbouring tracks. For practical reasons, the difference inperiodicity is selected to be even, e.g. 4, 6, 8, 16, 32, 48 or 64whereas the number of wobbles is about 3200 at the innermost zone. Byselecting such a low difference, the interference signal can becontrolled and the maximum interference can be located at predeterminedpositions. In an embodiment in the disc format with headers, whichformat is described above with reference to FIGS. 1a and 3, the maximuminterference can be located relative to the headers. In particular, themaximum interference is located as far as possible before the headers,so that, the headers can be reliably detected, because the phase lockedloop has ample signal to synchronize. Hence, in this embodiment the dischas the land groove format and the phase difference of the wobblesconfining a land between two adjoining zones is substantially zero nearthe headers. An advantageous choice is a difference of only one wobblein each track portion, so that the maximum interference can be locatedin the middle of the boundary track portion and the minimum at theheader.

FIG. 9 shows servo signals generated at a zone boundary. The firstsignal 91 has a number of periods n, and may be generated scanning thelast track of a zone for a full turn. The third signal 93 is generatedfrom the first track within the next zone, and has n+4 periods. Thesecond signal 92 is generated from the boundary track between two zones,and shows the interference from combining the servo signals of twodifferent wobble frequencies. As the difference in the number of periodsis 4, the signal shows an extinction 94 at 4 locations. The secondsignal 92 is generated when scanning an intermediate land between twozones having wobble grooves, so that the signal is the sum of twowobbles and complete extinctions occur. In a different embodiment, theinterference is caused by cross-talk of the neighbouring track, andpartial extinctions (amplitude variations) instead of completeextinctions occur. The boundary tracks may be skipped when recordingdata, or a phase locked loop may be controlled to keep in lock when a(partial) extinction 94 occurs.

Although the invention has been explained by embodiments using four oreight headers in each turn, it will be clear that other numbers or acombination of numbers can be employed in the invention. For instance, adisc of a recordable type has been described, but the invention can beapplied also to discs comprising recorded data, or discs of a read-onlytype. Further, the invention lies in each and every novel feature orcombination of features.

What is claimed is:
 1. An optical disc comprising a storage area forstoring data at a substantially constant storage density, the storagearea being subdivided into a plurality of coaxial annular zones withmultiple circular or spiral windings, each winding of multiple windingsin a zone being adapted to store a predetermined amount of data at apredetermined storage density of the winding, the winding havingperiodic characteristics which are radially aligned with the periodiccharacteristics of one or more adjacent windings of the same zone, theperiodic characteristics indicating the storage density of the winding.2. The disc of claim 1, wherein the periodic characteristics comprise aradial wobble associated with the windings.
 3. The disc of claim 2,wherein the storage area includes grooves and lands defining thewindings, the boundaries of the grooves exhibiting the radial windingwobble, and the wobble being aligned between grooves within one of thezones.
 4. The disc of claim 1, wherein the size of zones is such thatthe difference in the number of periodic characteristics between thewindings of adjoining zones is relatively low in relation to the numberof periodic characteristics in a winding.
 5. The disc of claim 4,wherein the difference in the number of periodic characteristics betweenwindings of adjacent zones is 1, 2, 4, 6, 8, 16, 32, 48 or
 64. 6. Thedisc of claim 1, wherein the winding of the storage area have a servopattern that includes headers alternating with storage portions, and aphase difference in the periodic characteristics between two windings ofdifferent adjoining zones is substantially zero near the headers.
 7. Thedisc of claim 6, wherein the difference in periodicity between adjoiningzones results in 1 or 2 extinctions within one winding portion.
 8. Thedisc of claim 1, wherein the storage area contains recorded data.
 9. Thedisc of claim 1, wherein the optical disc is of a read-only type.
 10. Arecorder comprising a recording head and means for controlling therecording head to record data in a storage area of an optical disc witha substantially constant storage density, the storage area beingsubdivided into a plurality of coaxial annular zones with multiplecircular or spiral windings, each winding of multiple windings in a zonebeing adapted to store a predetermined amount of data at a predeterminedstorage density of the winding, the winding having periodiccharacteristics which are radially aligned with the periodiccharacteristics of one or more adjacent windings of the same zone, theperiodic characteristics indicating the storage density of the winding.11. The recorder of claim 10, wherein the controlling means record apredetermined amount of channel bits for each instance of the periodiccharacteristics.
 12. The recorder of claim 10, wherein the controllingmeans control the speed of recording depending on the periodiccharacteristics.
 13. A player comprising a playing head and means forcontrolling the playing head to play data from in a storage area of anoptical disc with a substantially constant storage density, the storagearea being subdivided into a plurality of coaxial annular zones withmultiple circular or spiral windings, each winding of multiple windingsin a zone being adapted to store a predetermined amount of data at apredetermined storage density of the winding, the winding havingperiodic characteristics which are radially aligned with the periodiccharacteristics of one or more adjacent windings of the same zone, theperiodic characteristics indicating the storage density of the winding.14. The player of claim 13, wherein the controlling means retrieve datafrom an area of the winding following an unrecorded area by adjustingthe reading speed during scanning of the unrecorded area depending onthe periodic characteristics.
 15. The disc of claim 1, wherein theaverage of the storage densities of the windings within each zone aresubstantially equal to the constant storage density.
 16. The recorder ofclaim 10, wherein the average of the storage densities of the windingswithin each zone are substantially equal to the constant storagedensity.
 17. The player of claim 14, wherein the average of the storagedensities of the windings within each zone are substantially equal tothe constant storage density.
 18. The optical disk of claim 1, in which:the average of the storage densities of the windings within each zoneare substantially equal to the constant storage density; the availablestorage in windings of a same zone being substantially equal and theavailable storage in the windings of different zones being different;the periodic characteristics include a radial wobble associated with thewindings; the storage area includes grooves and lands defining thewindings, the boundaries of the grooves exhibiting the radial windingwobble, and the wobble being aligned between grooves within one of thezones; the size of zones is such that the difference in the number ofperiodic characteristics between the windings of adjoining zones isrelatively low in relation to the number of periodic characteristics ina winding; the difference in the number of periodic characteristicsbetween windings of adjacent zones is 1, 2, 4, 6, 8, 16, 32, 48 or 64;the storage area comprises grooves and lands both constituting thewindings, the grooves exhibiting the radial winding wobble, and thewobble being aligned between grooves within each one of the zones; thewindings of the storage area have a servo pattern that includes headersalternating with storage portions, and a phase difference in theperiodic characteristics between two windings of different adjoiningzones is substantially zero near the headers; a predetermined amountdata is stored in the storage portions for each instance of the periodiccharacteristics; the difference in periodicity between adjoining zonesresults in 1 or 2 extinctions within one winding portion; the storagearea contains data; and the optical disc is of a read-only type.
 19. Therecorder of claim 10, in which: the average of the storage densities ofthe windings within each zone are substantially equal to the constantstorage density; the available storage in windings of a same zone beingsubstantially equal and the available storage in the windings ofdifferent zones being different; the periodic characteristics include aradial wobble associated with the windings; the storage area includesgrooves and lands defining the windings, the boundaries of the groovesexhibiting the radial winding wobble, and the wobble being alignedbetween grooves within one of the zones; the size of zones is such thatthe difference in the number of periodic characteristics between thewindings of adjoining zones is relatively low in relation to the numberof periodic characteristics in a winding; the difference in the numberof periodic characteristics between windings of adjacent zones is 1, 2,4, 6, 8, 16, 32, 48 or 64; the storage area comprises grooves and landsboth constituting the windings, the grooves exhibiting the radialwinding wobble, and the wobble being aligned between grooves within eachone of the zones; the windings of the storage area have a servo patternthat includes headers alternating with storage portions, and a phasedifference in the periodic characteristics between two windings ofdifferent adjoining zones is substantially zero near the headers; apredetermined amount data is stored in the storage portions for eachinstance of the periodic characteristics; the difference in periodicitybetween adjoining zones results in 1 or 2 extinctions within one windingportion; the storage area contains data; the optical disc is of aread-only type; the controlling means record a predetermined amount ofchannel bits for each instance of the periodic characteristics; and thecontrolling means control the speed of scanning during recordingdepending on the periodic characteristics.
 20. The player of claim 14,in which: the average of the storage densities of the windings withineach zone are substantially equal to the constant storage density; theavailable storage in windings of a same zone being substantially equaland the available storage in the windings of different zones beingdifferent; the periodic characteristics include a radial wobbleassociated with the windings; the storage area includes grooves andlands defining the windings, the boundaries of the grooves exhibitingthe radial winding wobble, and the wobble being aligned between grooveswithin one of the zones; the size of zones is such that the differencein the number of periodic characteristics between the windings ofadjoining zones is relatively low in relation to the number of periodiccharacteristics in a winding; the difference in the number of periodiccharacteristics between windings of adjacent zones is 1, 2, 4, 6, 8, 16,32, 48 or 64; the storage area comprises grooves and lands bothconstituting the windings, the grooves exhibiting the radial windingwobble, and the wobble being aligned between grooves within each one ofthe zones; the windings of the storage area have a servo pattern thatincludes headers alternating with storage portions, and a phasedifference in the periodic characteristics between two windings ofdifferent adjoining zones is substantially zero near the headers; apredetermined amount data is stored in the storage portions for eachinstance of the periodic characteristics; the difference in periodicitybetween adjoining zones results in 1 or 2 extinctions within one windingportion; the storage area contains data; the optical disc is of aread-only type; the controlling means control the speed of scanningduring playing depending on the periodic characteristics; and thecontrolling means retrieve data from an area of the winding following anunrecorded area by adjusting the reading speed during scanning of theunrecorded area depending on the periodic characteristics.
 21. Anoptical disc comprising a storage area for storing data at asubstantially constant storage density, the storage area beingsubdivided into a plurality of coaxial annular zones with multiplecircular or spiral windings, the winding having periodic characteristicswhich are radially aligned with the periodic characteristics of one ormore adjacent windings of the same zone, the windings of the storagearea have a servo pattern that includes headers alternating with storageportions, and a phase difference in the periodic characteristics betweentwo windings of different adjoining zones is substantially zero near theheaders.
 22. A recorder comprising a recording head and means forcontrolling the recording head to record data in a storage area of anoptical disc with a substantially constant storage density, the storagearea being subdivided into a plurality of coaxial annular zones withmultiple circular or spiral windings, the winding having periodiccharacteristics which are radially aligned with the periodiccharacteristics of one or more adjacent windings of the same zone, thewindings of the storage area have a servo pattern that includes headersalternating with storage portions, and a phase difference in theperiodic characteristics between two windings of different adjoiningzones is substantially zero near the headers.
 23. A player comprising aplaying head and means for controlling the playing head to play datafrom in a storage area of an optical disc with a substantially constantstorage density, the storage area being subdivided into a plurality ofcoaxial annular zones with multiple circular or spiral windings, thewinding having periodic characteristics which are radially aligned withthe periodic characteristics of one or more adjacent windings of thesame zone, the windings of the storage area have a servo pattern thatincludes headers alternating with storage portions, and a phasedifference in the periodic characteristics between two windings ofdifferent adjoining zones is substantially zero near the headers.
 24. Arecorder comprising a recording head and means for controlling therecording head to record data in a storage area of an optical disc witha substantially constant storage density, the storage area beingsubdivided into a plurality of coaxial annular zones with multiplecircular or spiral windings, each winding of multiple windings in a zonebeing adapted to store a predetermined amount of data at a predeterminedstorage density of the winding, the winding having periodiccharacteristics which are radially aligned with the periodiccharacteristics of one or more adjacent windings of the same zone, thecontrolling means control the speed of scanning during recordingdepending on the periodic characteristics.
 25. A player comprising aplaying head and means for controlling the playing head to play datafrom in a storage area of an optical disc with a substantially constantstorage density, the storage area being subdivided into a plurality ofcoaxial annular zones with multiple circular or spiral windings, eachwinding of multiple windings in a zone being adapted to store apredetermined amount of data at a predetermined storage density of thewinding, the winding having periodic characteristics which are radiallyaligned with the periodic characteristics of one or more adjacentwindings of the same zone, the controlling means control the speed ofscanning during playing depending on the periodic characteristics.
 26. Amethod of producing an optical recording, comprising: providing anoptical disc with a storage area for storing data at a substantiallyconstant storage density, the storage area being subdivided into aplurality of coaxial annular zones with multiple circular or spiralwindings, each winding of multiple windings in a zone being adapted tostore a predetermined amount of data at a predetermined storage densityof the winding, the winding having periodic characteristics which areradially aligned with the periodic characteristics of one or moreadjacent windings of the same zone, the periodic characteristicsindicating the storage density of the winding; and recording data inconsecutive windings of the storage area of the optical disc.
 27. Amethod of producing an optical recording, comprising: providing anoptical disc comprising a storage area for storing data at asubstantially constant storage density, the storage area beingsubdivided into a plurality of coaxial annular zones with multiplecircular or spiral windings, the winding having periodic characteristicswhich are radially aligned with the periodic characteristics of one ormore adjacent windings of the same zone, the windings of the storagearea have a servo pattern that includes headers alternating with storageportions, and a phase difference in the periodic characteristics betweentwo windings of different adjoining zones is substantially zero near theheaders; and recording data in consecutive windings of the storage areaof the optical disc.